Can a blood test detect heart attack and heart failure?
Actually two tests are needed, one to check for heart attack and another to check for heart failure. The most commonly used blood test for heart attack is troponin estimation. For heart failure you can use either BNP (brain type natriuretic peptide) or NT-proBNP which is related protein. BNP precursor proBNP is stored in the ventricles. It is released when there is heart failure and cleaved by enzymes in the blood to BNP and NT-proBNP (N terminal proBNP). BNP is the active hormone while NT-proBNP is biologically inactive. But since NT-proBNP has a higher half life, it is better to test it rather than BNP.
Though you need two tests to check for heart attack and heart failure, there are point-of-care machines for use in the emergency department which can check both together with one blood sample. The machine gives the result in a short period of about 15 minutes, which is a great help in triaging patients in the emergency department. Patients with elevated troponin or NT-proBNP need higher levels of care and can be moved to the appropriate care area, usually the cardiac intensive care unit. Those with troponin elevation may benefit from early coronary angiography and revascularization (checking for blocks in the blood vessels of the heart and removing them if needed). NT-proBNP is useful to differentiate respiratory from cardiac causes of breathlessness. Both troponin and NT-proBNP may be falsely elevated in kidney failure. But checking for serial increase in levels may still be useful.
People can have heart attack and heart failure together as heart failure is an important complication of a heart attack. Then both tests are abnormal simultaneously. Having a heart attack with heart failure is obviously more dangerous than a heart attack without heart failure.